1. Field of the Invention
The present invention relates to equipment and a method for annealing semiconductors.
2. Description of the Prior Art
At present, the annealing technique is absorbing the attention of the semiconductor industry in two aspects. One is for the crystallization of a semiconductor element and the restoration of semiconductor crystals from damages which are caused, by the ion implantation of an impurity element; for example, phosphorus through the use of high energy into a silicon wafer with a view to providing the semiconductor element with a novel function. The most common traditional way of annealing is what is called the electric furnace method, in which the wafer is heated in an electric furnace 1 for example, at 1000.degree. C. for 30 minutes while supplying thereinto dry nitrogen. This method is simple, but it has such drawbacks as follows:
(a) it causes warps in the wafer, thus decreasing the yield in the ensuing processes; PA1 (b) as heating requires a prolonged time, the interior of the wafer is subject to changes in the implanted-ion distribution; PA1 (c) the surface of the wafer is apt to be contaminated; PA1 (d) a prolonged time is needed for annealing. PA1 (e) the distribution of the implanted ions is subject to substantial changes as their diffusion rate is extremely high in the liquid phase, though the restoration of semiconductor crystals from damages is effected because of the fusion of the wafer surface and the achievement of crystallization through the liquid epitaxial growth; PA1 (f) because the radiated light is of a single wavelength, there occurs an interference pattern in the melting area, leading to uneven irradiation of the wafer; PA1 (g) in the case of employing a continuous oscillation laser, the wafer is scanned by a small beam spot, resulting in producing a portion of insufficient annealing in the linear boundaries between scanning lines, and if the space between the scanning lines is reduced, then the scanning takes much time and often yields overheated portions, thus causing such a disadvantage as uneven irradiation; and PA1 (h) because of the laser light being of a single wavelength, an interference pattern is developed on the wafer surface to cause uneven irradiation thereof, and also as a common defect of the laser ray annealing, it calls for large and precise equipment and further advanced techniques for operation.
and
In view of these drawbacks, there is now being sought, as an alternative to this annealing method, the application of laser rays for brief exposure of the wafer thereto. Laser annealing, however, such as, in the case of using the pulse-oscillation laser, also has the following drawbacks:
The other annealing is for producing, for example, a silicon wafer by the epitaxial growth of a silicon layer which is deposited on a suitable substrate by means of the ion evaporation technique. The annealing, in such a case, was hitherto performed in the same manner as above mentioned, that is, in an electric furnace, or by exposing the wafer to the laser ray, and in this case, there are the same defects as previously mentioned.